The purpose of a device for suspending contact cable or a so-called "suspension unit" is to maintain the supporting cable and the contact cable in the correct position with respect to the rails. The supporting cable acts as an attachment for suspension wires that maintain the contact cable at a reasonably constant height above the rails. Both cables are under tension which is usually at a force of about 1-1.5 tonnes.
A known suspension unit for vehicles running on rails, particularly trains, generally includes an upper tension rod connected to a support mast, a compression rod connected to the support mast to hold up a free end of the tension rod, which carries a supporting cable and a lower horizontal rod that has a jointed link to the compression rod, with the horizontal rod supporting a joint direction rod where the contact cable is suspended at the free end. As this type of suspension unit has to be adjusted to different distances between the mast and the center of the rails, the rods are adjusted by being cut into suitable lengths before they are put together.
When known or conventional suspension units are used, they will consequently demand a considerable amount of preliminary adjustments which are usually carried out in a workshop, before being taken to the place where they are to be fitted. This is an expensive and time consuming process.
In a known type of suspension unit, the connection bracket for the supporting cable is jointed with the clamp connection between a tension rod and a compression rod. Adjustment of a length of the suspension unit, for example, the horizontal distance between the mast and where the supporting cable is attached, is thus restricted, difficult and time consuming.
Another known suspension unit utilizes a similar clamp connection between a tension rod and a compression rod and a separate movable attachment for the supporting cable on the tension rod. The horizontal adjustment of the supporting cable is thus easier, but an extra clamp is required which increases the cost. The vertical adjustment of the supporting cable point difficult and time-consuming with both these solutions.
When changing and refurbishing cables, trains have to be stopped while the existing lines are removed and replaced by new ones. This work is made more efficient by using special-purpose vehicles with lifting equipment designed for the removal of old suspension units; fitting, stretching and loading new cables. This work nevertheless partially involves manual handling of the suspension unit. Existing suspension units in this context have been unnecessarily complex and have created problems with respect to the regulations governing the work environment. A general problem with known solutions is that they are time-consuming to implement so that the effective working time on lines, which has to be done between each passing train, is extremely short. Existing suspension units also have a variety of connections and clamps, which results in a large inventory of costly equipment in storage and expensive material administration.